1 //===-- ProfilePaths.cpp - interface to insert instrumentation ---*- C++ -*--=//
3 // This inserts intrumentation for counting
4 // execution of paths though a given function
5 // Its implemented as a "Function" Pass, and called using opt
7 // This pass is implemented by using algorithms similar to
8 // 1."Efficient Path Profiling": Ball, T. and Larus, J. R.,
9 // Proceedings of Micro-29, Dec 1996, Paris, France.
10 // 2."Efficiently Counting Program events with support for on-line
11 // "queries": Ball T., ACM Transactions on Programming Languages
12 // and systems, Sep 1994.
14 // The algorithms work on a Graph constructed over the nodes
15 // made from Basic Blocks: The transformations then take place on
16 // the constucted graph (implementation in Graph.cpp and GraphAuxillary.cpp)
17 // and finally, appropriate instrumentation is placed over suitable edges.
18 // (code inserted through EdgeCode.cpp).
20 // The algorithm inserts code such that every acyclic path in the CFG
21 // of a function is identified through a unique number. the code insertion
22 // is optimal in the sense that its inserted over a minimal set of edges. Also,
23 // the algorithm makes sure than initialization, path increment and counter
24 // update can be collapsed into minmimum number of edges.
25 //===----------------------------------------------------------------------===//
27 #include "llvm/Transforms/Instrumentation/ProfilePaths.h"
28 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
29 #include "llvm/Support/CFG.h"
30 #include "llvm/Constants.h"
31 #include "llvm/DerivedTypes.h"
32 #include "llvm/iMemory.h"
37 struct ProfilePaths : public FunctionPass {
38 const char *getPassName() const { return "ProfilePaths"; }
40 bool runOnFunction(Function *F);
42 // Before this pass, make sure that there is only one
43 // entry and only one exit node for the function in the CFG of the function
45 void ProfilePaths::getAnalysisUsage(AnalysisUsage &AU) const {
46 AU.addRequired(UnifyFunctionExitNodes::ID);
50 // createProfilePathsPass - Create a new pass to add path profiling
52 Pass *createProfilePathsPass() {
53 return new ProfilePaths();
57 static Node *findBB(std::set<Node *> &st, BasicBlock *BB){
58 for(std::set<Node *>::iterator si=st.begin(); si!=st.end(); ++si){
59 if(((*si)->getElement())==BB){
66 //Per function pass for inserting counters and trigger code
67 bool ProfilePaths::runOnFunction(Function *M){
68 // Transform the cfg s.t. we have just one exit node
69 BasicBlock *ExitNode = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
71 // iterating over BBs and making graph
72 std::set<Node *> nodes;
75 Node *exitNode, *startNode;
77 // The nodes must be uniquesly identified:
78 // That is, no two nodes must hav same BB*
80 // First enter just nodes: later enter edges
81 for (Function::iterator BB = M->begin(), BE=M->end(); BB != BE; ++BB){
82 Node *nd=new Node(*BB);
90 // now do it againto insert edges
91 for (Function::iterator BB = M->begin(), BE=M->end(); BB != BE; ++BB){
92 Node *nd=findBB(nodes, *BB);
93 assert(nd && "No node for this edge!");
94 for(BasicBlock::succ_iterator s=succ_begin(*BB), se=succ_end(*BB);
96 Node *nd2=findBB(nodes,*s);
97 assert(nd2 && "No node for this edge!");
103 Graph g(nodes,edges, startNode, exitNode);
105 DEBUG(printGraph(g));
107 BasicBlock *fr=M->front();
109 // If only one BB, don't instrument
110 if (M->getBasicBlocks().size() == 1) {
111 // The graph is made acyclic: this is done
112 // by removing back edges for now, and adding them later on
115 DEBUG(cerr << "Backedges:" << be.size() << "\n");
117 // Now we need to reflect the effect of back edges
118 // This is done by adding dummy edges
119 // If a->b is a back edge
120 // Then we add 2 back edges for it:
121 // 1. from root->b (in vector stDummy)
122 // and 2. from a->exit (in vector exDummy)
123 vector<Edge> stDummy;
124 vector<Edge> exDummy;
125 addDummyEdges(stDummy, exDummy, g, be);
127 // Now, every edge in the graph is assigned a weight
128 // This weight later adds on to assign path
129 // numbers to different paths in the graph
130 // All paths for now are acyclic,
131 // since no back edges in the graph now
132 // numPaths is the number of acyclic paths in the graph
133 int numPaths=valueAssignmentToEdges(g);
135 // create instruction allocation r and count
136 // r is the variable that'll act like an accumulator
137 // all along the path, we just add edge values to r
138 // and at the end, r reflects the path number
139 // count is an array: count[x] would store
140 // the number of executions of path numbered x
141 Instruction *rVar=new
142 AllocaInst(PointerType::get(Type::IntTy),
143 ConstantUInt::get(Type::UIntTy,1),"R");
145 Instruction *countVar=new
146 AllocaInst(PointerType::get(Type::IntTy),
147 ConstantUInt::get(Type::UIntTy, numPaths), "Count");
149 // insert initialization code in first (entry) BB
150 // this includes initializing r and count
151 insertInTopBB(M->getEntryNode(),numPaths, rVar, countVar);
153 // now process the graph: get path numbers,
154 // get increments along different paths,
155 // and assign "increments" and "updates" (to r and count)
156 // "optimally". Finally, insert llvm code along various edges
157 processGraph(g, rVar, countVar, be, stDummy, exDummy);
160 return true; // Always modifies function